This invention relates to electrochemical cells. More particularly, it is concerned with electrochemical cells having an oxidizable active anode electrode, a cathode current collector, and an electrolytic solution comprising a reducible liquid cathode material, and an electrolyte solute dissolved therein.
A particularly effective class of electrochemical cells which employs soluble or liquid cathode materials, as opposed to the more conventional solid cathodes, has undergone rapid development in recent years. In these cells the active cathode material is usually a fluid solvent for an electrolyte solute which provides conductivity. The active anode electrode of the cell is usually of lithium or other highly electropositive metal. The solvent is usually a fluid oxyhalide, specifically thionyl chloride or sulfuryl chloride. During discharge of the cell the solvent is electrochemically reduced on a cathode current collector.
There are some problems which limit the usefulness of liquid cathode electrochemical cells. Among the problems are those relating to cell performance after prolonged storage and to their resistance to abusive treatment, such as short circuiting. During storage the lithium anode reacts with the liquid cathode material causing anode corrosion and passivation of the lithium metal. During accidental short circuiting relatively high internal temperatures may occur within the cell consequently increasing the rate of reaction between lithium and the liquid cathode material leading to still higher temperatures and the possibility of thermal runaway.
Various techniques have been employed to reduce the problems of anode corrosion and anode passivation, including coating the anode electrode with an organic polymer film. Techniques for coating anode electrodes with vinyl polymer films are discussed, for example, in U.S. Pat. Nos. 3,993,501, and 4,278,741 to Kalnoki-Kis. U.S. Pat. Nos. 4,170,693, and 4,296,185 to Catanzarite and U.S. Pat. Nos. 4,402,995, and 4,503,088 to Fleischer describe techniques of coating lithium anodes with cryanoacrylates. Although improvements in storage life and in reducing the problems of accidental circuits have been obtained in electrochemical cells fabricated in accordance with the teachings in the foregoing patents, it is desirable to improve further the characteristics of cells after prolonged storage and also to reduce further the problems of short circuits